Pregnancy calls for extra caution with essential oils, especially during the first trimester — most aromatherapists recommend avoiding all essential oils during the first 12 weeks. After the first trimester, oils generally considered safer include Roman chamomile, geranium, lavender, frankincense, tangerine, and grapefruit. However, a long list of oils should be completely avoided throughout pregnancy as they can stimulate uterine contractions or affect foetal development — these include clary sage, camphor, rosemary, cinnamon, basil, fennel, wintergreen, and thyme, among others. Always use very low dilutions (1% or less), diffuse only in well-ventilated spaces for short durations, and consult your OB-GYN or midwife before adding any essential oil to your routine.